Various processes and catalysts exist for the homopolymerization or copolymerization of olefins. For many applications, it is desirable for a polyolefin to have a high weight average molecular weight while having a relatively narrow molecular weight distribution. A high weight average molecular weight, when accompanied by a narrow molecular weight distribution, provides a polyolefin with, among other things, high strength properties.
Traditional Ziegler-Natta catalysts systems—a transition metal compound co-catalyzed by an aluminum alkyl—are typically capable of producing polyolefins having a high molecular weight, but with a broad molecular weight distribution.
More recently a catalyst system has been developed wherein the transition metal compound has two or more cyclopentadienyl ring ligands—such transition metal compound being referred to herein as a “metallocene—which catalyzes the production of olefin monomers to polyolefins. Accordingly, titanocenes, zirconocenes and hafnocenes, have been utilized as the transition metal component in such “metallocene” containing catalyst system for the production of polyolefins and ethylene-alpha-olefin copolymers.
Organometallics 1998, 17, 2155 discloses phosphorus bridged bis-cyclopentadienyl ligands with four bonds to the phosphorus bridge. Group 4 metals are not used.
J. Mol. Cat. A. 1998, 128, 245 discloses phosphorus bridged ligands with three bonds to the phosphorus ligand. Compounds include PhP(fluoreyl)(cyclopentadienyl)ZrCl2, PhP(fluorenyl)2ZrCl2, 1,1′-PhP(2-methyl-4-phenylindenyl)2ZrCl2 (bridged in the one position), 1,1′-iso-propylP(PhP(2-methyl-4-phenylindenyl)2ZrCl2 (bridged in the one position), 1,1′-PhP(indenyl)2ZrCl2 (bridged in the one position).
J. Organomet. Chem. 1998, 568, 127 discloses phosphorus bridged ligands with three bonds to the phosphorous ligand. Compounds include PhP(fluorenyl)2ZrCl2, and PhP(fluorenyl)2HfCl2. The paper also discloses some additional ligand preps, but not with bridges in the 2-position of the indenyl ligand. Polymerization data is included.
Organometallics 1999, 18, 6 discloses phosphorous bridged bis-cyclopentadienyl Group 4 metallocenes with three or four bonds to the phosphorous ligand (e.g. Cp*2PMe, Cp*2PMe(E) with S═O, S, Se). There is a note in the paper stating that the compounds are active polymerization catalysts when activated by MAO.
Z. Naturforsch., B 1999, 54, 482 discloses phosphorous bridged bis-cyclopentadienyl complexes.
Organometallics 2000, 19, 5155—Discloses phosphorous bridged bis-cyclopentadienyl Group 4 metallocenes with 4 bonds to the phosphorous ligand (e.g. Cp*2PMe2). This makes the metallocene ionic as in [Me2PCp*2ZrCl2]+[I]−. There is no mention of polymerization.